1. Field of the Invention
The present invention relates to a printing plate making apparatus and a printing plate making method.
2. Description of the Related Art
There is known a printing plate making apparatus including a drum being provided at its outer peripheral surface with a recording plate (recording medium) and being rotated in a horizontal scanning direction, and a two-dimensional image on the recording plate being engraved t (recorded) on the recording plate by scanning the recording medium in a vertical scanning direction that is perpendicular to the horizontal direction with a laser beam in accordance with image data of an image that is to be engraved.
In the above printing plate making apparatus, when a relief printing plate such as a flexographic printing plate and an intaglio printing plate such as a gravure is directly engraved by laser beam, it is required to satisfy both reproducibility of fine line or mesh point in shallow engraving (precision engraving) when engraving a narrow region and deep engraving (rough engraving) when engraving a wide region.
Since it is generally difficult to satisfy both two requirements at the same time, there is known a method in which laser beam having a small spot diameter for shallow engraving (precision engraving) and high power laser beam for deep engraving (rough engraving) are provided, and engraving is carried out using these laser beams separately (e.g., U.S. Pat. No. 6,150,629, U.S. Patent Application Laid-Open No. 2006/0279794A1, and Japanese Patent Application Laid-Open (JP-A) No. 2005-224481).
When printing is carried out using a relief printing plate such as a flexographic printing plate, if an edge shape of a convex portion formed on the plate is obtuse or a foundation which supports the convex portion is weak, printing density is varied by a pressing force against a printing medium, fine line or highlight point is not clearly printed or clear print is not carried out in some cases.
To reduce these problems, it is proposed to form a region remaining in convex shape such that a convex portion having rectangular cross section is formed on top of a foundation having a trapezoidal cross section (see JP-A No. 6-234262). To directly engraving a relief printing plate by laser beams at a higher speed, it is proposed to engrave a recording medium by exposing the recording medium to a light twice (see Japanese Patent No. 35562044).